12 research outputs found
A model-independent analysis of the dependence of the anomalous J/psi suppression on the number of participant nucleons
A recently published experimental dependence of the J/psi to Drell-Yan ratio
on the measured, by a zero degree calorimeter, forward energy E_ZDC in Pb+Pb
collisions at the CERN SPS is analyzed. Using a model-independent approach it
is shown that the data are at variance with an earlier published experimental
dependence of the same quantity on the transverse energy of neutral hadrons
E_T. The discrepancy is related to a moderate centrality region: 100 < N_p <
200 (N_p is the number of participant nucleons) and is peculiar only to the
data obtained within the `minimum bias' analysis (using the `theoretical
Drell-Yan'). This could result from systematic experimental errors in the
minimum bias sample. A possible source of the errors is discussed.Comment: 10 pages, LaTeX, 3 PS-figures. V2: Misprints are correcte
Hadronic centrality dependence in nuclear collisions
The kaon number density in nucleus+nucleus and p+p reactions is investigated
for the first time as a function of the initial energy density and
is found to exhibit a discontinuity around =1.3 GeV/fm. This
suggests a higher degree of chemical equilibrium for
1.3 GeV/fm. It can also be interpreted as reflection of the same
discontinuity, appearing in the chemical freeze out temperature (T) as a
function of . The dependence of (u,d,s) hadrons,
whith N the number of participating nucleons, also indicates a high degree of
chemical equilibrium and T saturation, reached at 1.3 GeV/fm.
Assuming that the intermediate mass region (IMR) dimuon enhancement seen by
NA50 is due to open charm (), the following observation can be made:
a) Charm is not equilibrated. b) suppression -unlike
- appears also in S+A collisions, above 1
GeV/fm. c) Both charm and strangeness show a discontinuity near the same
. d) could be formed mainly through coalescence.
e) The enhancement factors of hadrons with u,d,s,c quarks may be connected in a
simple way to the mass gain of these particles if they are produced out of a
quark gluon plasma (QGP). We discuss these results as possible evidence for the
QCD phase transition occuring near 1.3 GeV/fm.Comment: 4 pages, 4 figures, proceedings of Vth International Conference on
Strangeness in Quark Matter, 20-25 July 2000, Berkeley, California. To appear
in Journal of Physics G: Nuclear and Particle Physic
Importance of reaction volume in hadronic collisions: Canonical enhancement
We study the canonical flavor enhancement arising from exact conservation of
strangeness, and charm flavor. Both the theoretical motivation, and the
practical consequences are explored. We argue using qualitative theoretical
arguments and quantitative evaluation, that this proposal to reevaluate
strangeness signature of quark--gluon plasma is not able to explain the
majority of available experimental results.Comment: 14 pages including 6 figures, submitted to Journal of Physics G
Presented at: Strange Quark Matter, September 2001, Frankfur
Open Charm Enhancement in Pb+Pb Collisions at SPS
The statistical coalescence model for the production of open and hidden charm
is considered within the canonical ensemble formulation. The data for the
J/\psi multiplicity in Pb+Pb collisions at 158 A GeV are used for the model
prediction of the open charm yield. We find a strong enhancement of the open
charm production, by a factor of about 2--4, over the standard hard-collision
model extrapolation from nucleon-nucleon to nucleus-nucleus collisions. A
possible mechanism of the open charm enhancement in A+A collisions at the SPS
energies is proposed.Comment: 4 pages, Late
Effective hadronic Lagrangian for charm mesons
An effective hadronic Lagrangian including the charm mesons is introduced to
study their interactions in hadronic matter. Using coupling constants that are
determined either empirically or by the SU(4) symmetry, we have evaluated the
absorption cross sections of and the scattering cross sections of
and by and mesons.Comment: 5 pages, 4 eps figures, presented at Strangeness 2000, Berkeley. Uses
iopart.cl
The High E_T Drop of J/psi to Drell-Yan Ratio from the Statistical c anti-c Coalescence Model
The dependence of the J/psi yield on the transverse energy E_T in heavy ion
collisions is considered within the statistical c anti-c coalescence model. The
model fits the NA50 data for Pb+Pb collisions at the CERN SPS even in the
high-E_T region (E_T > 100 GeV). Here E_T-fluctuations and E_T-losses in the
dimuon event sample naturally create the celebrated drop in the J/psi to
Drell-Yan ratio.Comment: 14 pages, REVTeX, 1 PS-figure. v2: References are corrected and
update
Charm in nuclear reactions in sqrt(s)=17 and 19 GeV
Consequences resulting from the D Dbar excess derived indirectly by the NA50
experiment in S+U and Pb+Pb collisions at sqrt(s)=19, 17 GeV, relevant for the
identification of the QCD phase transition in these collisions, are discussed.
The dependence of open and closed charm yields in Pb+Pb collisions on the
number of participating nucleons (N) indicates non thermal charm production and
J/Psi dissociation, stronger than the absorption seen in any other elementary
hadron. The J/Psi in central Pb+Pb collisions could originate dominantly from c
cbar pair coalescence out of a hadronizing quark and gluon environment.
Furthermore, the J/Psi appears to be suppressed in S+U collisions at sqrt(s)=19
GeV, as opposed to current interpretations. A significant change in the
(J/Psi)/D Dbar ratio as well as in the number density of kaons is observed
above energy density approx. 1 GeV/fm^3, suggesting a change of phase at this
energy density, and underlining the importance of direct open charm
measurements.Comment: (23 pages, 7 figures
Centrality and dE_{T}/d\etadN_{ch}/d\eta$ in Heavy Ion Collisions at Mid-Rapidity
The PHENIX experiment at RHIC has measured transverse energy and charged
particle multiplicity at mid-rapidity in Au + Au collisions at
= 19.6, 130, 62.4 and 200 GeV as a function of centrality. The presented
results are compared to measurements from other RHIC experiments, and
experiments at lower energies. The dependence of
and per pair of participants is consistent with logarithmic
scaling for the most central events. The centrality dependence of
and is similar at all measured incident
energies. At RHIC energies the ratio of transverse energy per charged particle
was found independent of centrality and growing slowly with . A
survey of comparisons between the data and available theoretical models is also
presented.Comment: Proccedings of the Workshop: Focus on Multiplcity at Bari, Italy,
June 17-19,2004. To be submitted to the Jornal of Physics, "Conference
series". Includes: 20 Pages, 15 figures, 3 Tables, 80 Referencie